Laryngotracheal stenosis (LTS) may occur secondary to congenital disorders, acute trauma, chronic inflammation, or prolonged intubation. LTS comprises the airway and may impair phonation, deglutition, and protection from aspiration. A wide variety of surgical techniques for the correction of LTS have been proposed, none of which has been universally successful. The Rotary Door Flap (RDF) is one such technique which utilizes a 180 (degree) rotation of a bipedicled, vascularized, myocutaneous flap composed of one of the infrahyoid muscles, the sternohyoid muscle (SH). Despite many advantages, especially excellent phonatory, ventilatory, and swallowing function postoperatively, the use of RDF continues to be limited secondary to concerns of inspiratory flap prolapse with airway comprise. Although clinical experience subjectively supports adequate RDF stability in the majority of cases, preliminary quantitative data demonstrates relative instability of the RDF with physiological airway pressures. Therefore, this research proposes to investigate the legitimacy of concerns for flap instability and investigate the efficacy of ancillary support measures in enhancing RDF stability. To determine the stability of the RDF in a previously established model of the human procedure, LTS will be induced in canine study subjects, the RDF reconstruction will be performed with or without an ancillary support procedure, and the subsequent stability of the RDF will be determined. Twenty four dogs will be divided into four study groups. To obtain baseline information concerning SH muscle recruitment, EMG's of the SH will be obtained in control group subjects with normal respiration and with increased upper airway resistance. Chronic laryngeal and tracheal stenosis will be established in all animals by electrocautery injury to the mucosa, perichondrium, and underlying cartilage of the larynx and trachea. At this time, animals assigned to the experimental groups will undergo injection of hydroxyapatite cement or implantation of titanium steel screen or porous polyethylene into the planned reconstructive flap. Subjects assigned to the control group will not receive additional supportive measures. Thirty days later, all animals will undergo the RDF reconstruction. Sixty days following the reconstruction, the airway will be observed and recorded endoscopically. To investigate the role of SH muscle contraction with stiffening in RDF stability, EMG studies of the SH of control group subjects will again be recorded during all phases of respiration. Study subjects will be sacrificed, the laryngotracheal complexes will be resected, and the amount of negative pressure (mmHg) required to cause 25% and 50% occlusion of the airway lumen at the level of the RDF will be determined. This data will allow statistical comparison of study groups as well as analysis of RDF stability with expected physiologic airway pressures. Permanent histologic sections of the RDF region will be prepared to determine the response to the ancillary support materials. Thus electromyographic, physiologic, and histologic data which is objective and quantitative will be obtained. This information will be utilized to provide clinical guidance concerning the use of the RDF as well as the application of the ancillary support procedures in the RDF and other reconstructive procedures.